Dielectric line and production method therefor

ABSTRACT

A dielectric line having a sufficient ensured strength and being suitable for mass production and a production method therefor are provided. The production method is a method for manufacturing a dielectric line having a dielectric strip which is provided between two conductive plates approximately parallel to each other and which has a width smaller than that of the conductive plates, and dielectric medium layers which are filled between the conductive plates other than the dielectric strip and which is composed of a porous material having a dielectric constant smaller than that of the dielectric strip. The dielectric line (NRD guide) is produced by film forming steps S 11  and S 12  in which a film of a dielectric raw material is formed on one of the conductive plates, a strip exposure step S 13  in which a part of the above film having a shape corresponding to the dielectric strip is exposed to predetermined light, beams, or vapor, and pore forming steps S 15  and S 16  in which the entire film of the dielectric raw material is made porous.

TECHNICAL FIELD

The present invention relates a dielectric line and a production methodtherefor, the dielectric line having superior strength properties andtransmission properties of high frequency signals and being suitable formass production.

BACKGROUND ART

Heretofore, for integrated circuits which require transmission of highfrequency signals in a millimeter wave band, microstrip lines,dielectric lines, and waveguide lines, and the like have been used. Inparticular, since a nonradiative dielectric line (NRD guide), which isone type of dielectric line and has been disclosed in Japanese ExaminedPatent Application Publication No. 1-51202, can suppress radiation lossof energy, superior transmission properties of high frequency signalscan be obtained.

FIG. 7 shows the structure of a general NRD guide 10. The conventionaland general NRD guide 10 has the structure in which two conductiveplates 1 and 2 approximately parallel to each other sandwich adielectric strip 4 having a width smaller than that of the conductiveplates 1 and 2. Parts 3 between the two conductive plates 1 and 2 otherthan the dielectric strip 4 are voids (air). As described above, in theconventional NRD guide 10, since the width of the dielectric strip 4 issmaller than the width of the conductive plates 1 and 2, and the contactarea therebetween is small, when the NRD guide 10 is handled, it isdifficult to ensure the strength to retain the structure describedabove. Techniques for ensuring the strength of the NRD guide 10 havebeen disclosed in Japanese Unexamined Patent Application PublicationNos. 3-270401, 6-45807, and 8-65015.

For example, in Japanese Unexamined Patent Application Publication No.3-270401, in order to increase the contact area between the conductiveplate and the dielectric strip, a technique has been disclosed in whichthe dielectric strip is formed to have an H-shaped cross-section. Inaddition, in Japanese Unexamined Patent Application Publication No.6-45807, a technique in which dams are provided for the conductiveplates along the dielectric strip has been disclosed; and in JapaneseUnexamined Patent Application Publication No. 8-65015, a technique hasbeen disclosed in which projections are provided on a surface of thedielectric strip to be bonded to the conductive plate and are thenburied therein. Accordingly, when the dielectric strip and theconductive plate are bonded to each other, the alignment can be easilyperformed, and the displacement of the bonding portion can be prevented.

In addition, in Japanese Unexamined Patent Application Publication No.6-260814, a technique has been disclosed in which in order to improvethe productivity of the NRD guides, top-half parts and bottom-half partsare produced separately and are then assembled into the NRD guides, andin Japanese Unexamined Patent Application Publication No. 2001-7611, atechnique has been disclosed in which as a method suitably used for massproduction of the NRD guides, a resist process is used.

However, according to the conventional structures and production methodsof the NRD guides described above, various machining steps must beperformed for the conductive plates and the dielectric strip, and as aresult, there has been a problem in that those mentioned above cannot besuitably applied to mass production.

In addition, there has been a limit to ensure the strength by thebonding portions between the two conductive plates and the dielectricstrip, and hence there has been a problem in that a sufficient strengthcannot be obtained.

Hence, the present invention was made in consideration of the situationsdescribed above, and an object of the present invention is to provide adielectric line and a production method therefor, the dielectric linecapable of ensuring a sufficient strength and being suitable for massproduction.

DISCLOSURE OF INVENTION

In order to achieve the object described above, the present inventionprovides a dielectric line which has a dielectric strip provided betweentwo conductive plates approximately parallel to each other and having awidth smaller than that of the conductive plates. In this dielectricline described above, the dielectric strip is composed of a porousmaterial, and the other parts between the two conductive plates otherthan the dielectric strip are filled with dielectric medium layerscomposed of a porous material having a dielectric constant smaller thanthat of the dielectric strip.

In the dielectric line described above, the dielectric constant of thedielectric strip is preferably 1.5 times or more the dielectric constantof the dielectric medium layer.

By the structure as described above, since the dielectric strip and thedielectric medium layers are filled between the two conductive plates,compared to a conventional dielectric line (see FIG. 7) in which theparts other than the dielectric strip are voids (air), the dielectricstrip is unlikely to be displaced, and as a result, the strength issignificantly increased, thereby forming a stable structure.

In addition, since the porous materials are used for the dielectricstrip and the dielectric medium layers, by increasing the porositythereof, the dielectric constant and the dielectric loss can besignificantly decreased, and as a result, high frequency signals can betransmitted with very high transmission efficiency (low loss).

In addition, the case may also be considered in which the dielectricstrip and the dielectric medium layers are formed of a substantiallyidentical material and have different porosities from each other. Inthis case, when the distance between the two conductive plates is formedto be one-half or less the wavelength of a signal in the dielectricmedium layer, the signal being transmitted through the dielectric line,an NRD guide (nonradiative dielectric line) can be formed in whichunnecessary radiation of transmission signals does not occur.Accordingly, more efficient signal transmission can be performed.

In order to ensure the nonradiative properties (confining effect of thedielectric strip), the difference in dielectric constant between thedielectric strip and the dielectric medium layer is important. In ageneral dielectric body, the dielectric constant has a predeterminedvalue which is determined by the material thereof; hence, when thedifference in dielectric constant is to be adjusted, a plurality ofdielectric materials must be used. However, in the case of porousdielectrics, even when the identical material is used, the dielectricconstant thereof depends on the porosity (the higher the porosity, thelower the dielectric constant); hence, by adjusting the porosity, thedielectric strip and the dielectric medium layers can be formed. Theterm “identical” substantially means that primary materials areidentical with each other, and slight difference in component caused bydifferent production conditions (drying condition and the like) is alsoincluded substantially in the scope of the “identical” (hereinafter, theabove term is to be construed as described above). As described above,when the dielectric constant is adjusted by changing the porosity, thedielectric strip and the dielectric medium layers can be formed from onetype of material, and hence the production can be easily performed(reduction in production cost). In addition to that described above,since the production can be performed using a patterning process,compared to the conventional case in which a three-dimensional structureis produced by machining or the like, the mass production can besuitably performed, and complicated shapes can also be produced.Furthermore, since the porosity can be freely determined, an optionaldielectric constant can be realized. As a result, since dielectricstrips having optional dielectric constants can be formed on onesubstrate (conductive plate), an NRD guide capable of responding totransmission signals having different frequencies can be formed on onesubstrate. (Heretofore, a plurality of dielectric materials which havedifferent dielectric constants from each other is necessarily disposed,and in some cases, since a dielectric material having a desireddielectric constant was not present, an NRD guide responding to thefrequency of a specific transmission signal could not be formed.)Accordingly, the degree of freedom of designing the NRD guide issignificantly increased.

In addition, as a material for the dielectric strip and the dielectricmedium layers, for example, an aerogel material may be mentioned.

In addition, the present invention also provides a method for producingthe dielectric line described above. This is, the method is a method forproducing a dielectric line having a dielectric strip provided betweentwo conductive plates approximately parallel to each other and having awidth smaller than that of the conductive plates, and dielectric mediumlayers filled between the conductive plates other than the dielectricstrip and composed of a porous material having a dielectric constantsmaller than that of the dielectric strip. The method described abovehas a film forming step of forming a film on one of the conductiveplates using a dielectric raw material, a strip exposure step ofexposing a part of the film of the dielectric raw material topredetermined light, beams, and vapor, the part having a shapecorresponding to the dielectric strip, and a pore forming step of makingthe entire film of the dielectric raw material porous.

Accordingly, compared to the part which is processed by the exposurestep, that is, to the part having a shape corresponding to thedielectric strip, the other parts which are not processed by theexposure process (that is, the parts corresponding to the dielectricmedium layers) have a high porosity, and as a result, the dielectricstrip and the dielectric medium layers can be formed so as to havewell-balanced dielectric constants, that is what required as thedielectric line.

In the film formed in the film forming step described above, chemicalbonds of the material itself are not substantially formed before thestrip exposure step is performed, and hence the film is in an incompletestate. When the strip exposure step is performed for the film in thestate described above, chemical reaction (polymerization reaction andthe like) is facilitated in the exposed part as compared to that in theparts which are not exposed. Hence, the difference in density occursbetween the part having a shape corresponding to the dielectric strip,which is processed by the strip exposure step, and the other parts(parts corresponding to the dielectric medium layers), and as a result,by the subsequent pore forming step, the difference in porosity occurstherebetween. This difference in porosity causes the difference indielectric constant, and as a result, the dielectric line is formed. Inaddition, after the strip exposure step is performed, even when thechemical reaction (chemical bonding) of the entire film including theparts other than the dielectric strip is facilitated by heat treatment,the chemical reaction caused by the heat treatment is moderate ascompared to that by the strip exposure step, and hence the difference indensity also occurs between the part having a shape corresponding to thedielectric strip and the other parts.

In addition, unlike the conventional production method in whichconstituent elements are separately formed, followed by assemblythereof, production can be performed by patterning, and hence massproduction of the dielectric lines is suitably performed.

As the strip exposure step described above, a step may be mentioned inwhich the part having a shape corresponding to the dielectric strip isexposed to ultraviolet rays, electron beams, X-rays, or ion beams, andin this case, the dielectric raw material may contain a photosensitivematerial. Alternatively, as the strip exposure step, a step may bementioned in which the part having a shape corresponding to thedielectric strip is exposed to moisture vapor, vapor containing anacidic material, vapor containing a basic material, or vapor containinga dielectric raw material. By any one of the methods described above,the difference in porosity after the pore forming step can be obtained.

In addition, in the method for producing a dielectric line describedabove, the substantially identical material is used for the dielectricstrip and the dielectric medium layers; however, the present inventionis not limited thereto, and different materials may also be used in somecases.

For example, there is provided a method for producing a dielectric linehaving a dielectric strip provided between two conductive platesapproximately parallel to each other and having a width smaller thanthat of the conductive plates, and dielectric medium layers filledbetween the conductive plates other than the dielectric strip andcomposed of a porous material having a dielectric constant smaller thanthat of the dielectric strip. The method described above has a firstfilm forming step of forming a first film on one of the conductiveplates using a first dielectric raw material, a film removing step ofremoving the first film except for a part having a shape correspondingto the dielectric strip, a second film forming step of forming a secondfilm using a second dielectric raw material on said one of the twoconductive plates which is processed by the film removing step, and apore forming step of making porous the entire films of the first and thesecond dielectric raw materials.

Accordingly, after the first film of the first dielectric raw materialis formed to have the shape of the dielectric strip in the first filmforming step and the film removing step, the parts corresponding to thedielectric medium layers are formed by the second film of the seconddielectric raw material in the second film forming step. By theproduction method described above, the dielectric line can also beformed.

In addition, as the film removing step, for example, there may bementioned a step in which, in the first film of the first dielectric rawmaterial, after the part having a shape corresponding to the dielectricstrip is exposed to predetermined light or beams, followed bydevelopment treatment, the other parts other that the part having ashape corresponding to the dielectric strip are removed.

As described above, in the film formed in the above film forming step,chemical bonds are not substantially formed before the strip exposurestep is performed, and the film is in an incomplete state. That is,since having a low molecular weight, the film is soluble in varioussolvents (organic solvents and alkaline solvents). Accordingly, afterthe part having a shape corresponding to the dielectric strip is exposedto the light or beams described above so as to facilitate the formationof chemical bonds, the parts other than the part (part exposed to thelight or beams) having a shape corresponding to the dielectric strip canbe selectively removed by development treatment.

In this case, when the first dielectric raw material contains aphotosensitive material, it is preferable since the exposure effect tolight or beams in the film removing step can be easily obtained.

Of course, light or beams having sufficient energy may be used in orderto facilitate the chemical reaction (polymerization reaction) ofmolecules in the film; however, when the photosensitive material is usedas described above, the exposure amount of light or beams can bereduced, and as a result, various advantages, such as decrease in timefor treatment and easy treatment using a simple device, can be obtained.

In addition, as the photosensitive material, for example, a photo-acidgenerator may be mentioned.

As the dielectric raw material, for example, a raw material containingan organic metal material may be mentioned. As the organic metalmaterial, a metal alkoxide may be mentioned by way of example.

In addition, as the dielectric raw material, a raw material containing asurfactant may also be mentioned.

As described above, when a surfactant is contained, surfactant micellesregularly disposed in a dielectric film are formed. By performing thepore forming step (that is, the step of removing the surfactant in thefilm) for the dielectric film as described above, pores regularlydisposed are formed. As a result, the mechanical strength of a porousstructure is enhanced, and hence the machinability of the film isimproved.

In addition, as the pore forming step, for example, a step of exposingthe dielectric raw material to a supercritical fluid may be mentioned.

As the pore forming step (the step of removing the surfactant in thefilm), for example, a step of exposing the film to an alcohol-basedorganic solvent having a high polarity may be mentioned; however, by thestep of exposing the film to the supercritical fluid having a lowsurface tension, the supercritical fluid can be diffused into very fineareas, and as a result, the surfactant even in very fine areas can beeffectively removed.

In the case described above, as the supercritical fluid, for example,carbon dioxide, ethanol, methanol, water, ammonia, and a fluorinatedcarbon material may be used alone or in combination.

Furthermore, when the pore forming step includes a step of performingheat treatment following the step of exposing the dielectric rawmaterial to a supercritical fluid, the film quality can be stabilized.

In the case described above, for example, the heat treatment in the poreforming step may be performed at 200° C. or more.

Accordingly, for example, when the film is formed of a silica material(one example of a dielectric raw material), Si—O bonds are enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the structure of a dielectric lineX of an embodiment according to the present invention.

FIG. 2 is a graph showing the relationship between the porosity and therelative dielectric constant of a porous material.

FIG. 3 is a flowchart showing the procedure of a production method ofthe dielectric line X of an embodiment according to the presentinvention.

FIG. 4 is a flowchart showing the procedure of a production method ofthe dielectric line X of a first example according to the presentinvention.

FIG. 5 is a flowchart showing the procedure of a production method ofthe dielectric line X of a second example according to the presentinvention.

FIG. 6 is a flowchart showing the procedure of a production method ofthe dielectric line X of a third example according to the presentinvention.

FIG. 7 is a perspective view showing the structure of a conventionalgeneral NRD guide.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiment and examples of the present invention will bedescribed in order to facilitate the understanding of the presentinvention. The following embodiment and examples of the presentinvention will be described by way of example, and it is naturally to beunderstood that the present invention is not limited thereto.

In this embodiment, FIG. 1 is a perspective view showing the structureof a dielectric line X of an embodiment according to the presentinvention; FIG. 2 is a graph showing the relationship between theporosity and the relative dielectric constant of a porous material; FIG.3 is a flowchart showing the procedure of a production method of thedielectric line X of an embodiment according to the present invention;FIG. 4 is a flowchart showing the procedure of a production method ofthe dielectric line X of a first example according to the presentinvention; FIG. 5 is a flowchart showing the procedure of a productionmethod of the dielectric line X of a second example according to thepresent invention; FIG. 6 is a flowchart showing the procedure of aproduction method of the dielectric line X of a third example accordingto the present invention; and FIG. 7 is a perspective view showing thestructure of a conventional general NRD guide.

First, referring to FIG. 1, the structure of the dielectric line X ofthe embodiment according to the present invention will be described.

As shown in FIG. 1, the dielectric line X has the structure composed oftwo conductive plates 1 and 2 and a dielectric strip 40 which isprovided therebetween and which has a width smaller than that of theconductive plates 1 and 2, and the structure described above is the sameas that of the conventional dielectric line (NRD guide) shown in FIG. 7;however, the points different therefrom are as follows. That is, thedielectric strip 40 is formed of a porous material, and parts which arebetween the conductive plates 1 and 2 other than the dielectric strip 40are filled with dielectric medium layers 30 composed of a porousmaterial having a dielectric constant smaller than that of thedielectric strip 40.

Since the dielectric strip 40 and the dielectric medium layers 30 arefilled between the two conductive plates 1 and 2 as described above,compared to the dielectric line which has been primarily used (shown inFIG. 7, in which the parts other than the dielectric strip are voids(air)), the displacement of the dielectric strip 40 is unlikely tooccur, and the strength is significantly enhanced to form a stablestructure.

In addition, since the porous materials are used for the dielectricstrip 40 and the dielectric medium layers 30, by increasing the porositythereof, the dielectric constant and the dielectric loss can beconsiderably decreased, and as a result, high frequency signals can betransmitted with very high transmission efficiency (low loss).Furthermore, by optionally selecting the porosity of the porousmaterial, a desired dielectric constant can be realized (see FIG. 2),and hence the degree of freedom of designing is significantly increased.

FIG. 2 is a graph showing the relationship between the porosity and thedielectric constant of a dielectric film formed of a metal alkoxide(tetramethoxysilane) as a raw material, the dielectric film being oneexample of a porous material. As shown in FIG. 2, it is understood thatas the porosity is increased, the relative dielectric constant linearlyapproaches 1.00. That is, when the porosity of the porous material isinfinitely increased to 100%, properties (relative dielectric constantand dielectric loss) can be obtained which are infinitely close to theproperties of air.

In addition, the distance between the two conductive plates 1 and 2(that is, the thickness of the dielectric strip 40 and that of thedielectric medium layers 30) is formed to be one-half or less thewavelength of a signal in the dielectric medium layer 30, the signalbeing transmitted through this dielectric line X. Hence, the dielectricline X forms an NRD guide (nonradiative dielectric line) in whichunnecessary radiation of transmission signals does not occur.Accordingly, efficient signal transmission having no radiation loss canbe performed.

Next, referring to the flowchart shown in FIG. 3, one example of aproduction method of the dielectric line X shown in FIG. 1 will bedescribed. Hereinafter, S11, S12, . . . each indicate the ordinal numberof a process step (step).

First, a dielectric raw material A, which is a predetermined dielectricraw material, is applied to a substrate which is the conductive plate 1,one of the two conductive plates described above, so as to have apredetermined thickness (S11). This thickness is one-half or less thewavelength of a signal in the dielectric medium layer 30, the signalbeing transmitted through the dielectric line X.

The dielectric raw material A is a solution prepared by the followingprocedure. That is, after 2 g of tetramethoxysilane (metal alkoxide)Si(CH₃O)₄, which is one example of an organic metal compound), 10 g ofethanol, 2 g of butanol, 1 g of methyl 3-methoxypropionate, and 1.2 g ofwater at a pH of 3 are mixed and stirred, the mixture thus prepared isheld at 60° C. for approximately 6 hours for facilitating reactionthereof to form a solution, a transparent solution is then prepared bymixing the above solution with IBCF (manufactured by Sanwa Chemical Co.,Ltd.), which is a photo-acid generator, at a ratio of 0.05% (percent byweight), and subsequently, 0.2 g of hexadecyltrimethylammonium chloride(one example of a surfactant) is mixed with 10 cc of the above solution,followed by stirring.

Next, a part coated with the dielectric raw material A described aboveis dried by heating (baking) at 80° C. in the air, so that the film ofthe dielectric raw material A is formed (S12). This heating is performedfor a sufficient period of time (such as approximately 1 to 5 minutes)to remove an excess solvent (necessary for coating but unnecessarythereafter) such as ethanol contained in the raw material solution andto stabilize the film on the substrate by increasing the viscosity ofthe film. In this embodiment, S11 and S12 are one example of the filmforming step.

Subsequently, only a part of the film of the above dielectric rawmaterial A, which has a shape corresponds to the dielectric strip 40, isirradiated with electron beams (that is, the part having a shapecorresponding to the dielectric strip 40 is exposed to electron beams)(S13). As the electron beams, for example, electron beams at anacceleration voltage of 50 keV and a dose of 10 μC/cm² are used.

Accordingly, Si—OH bonds formed from tetramethoxysilane are formed intoSi—O bonds (a so-called crosslinking reaction).

That is, the film formed before the irradiation of electron beams hasnot an ideal silica structure and still has many unreacted portions (inparticular, Si—OH bonds). When the film in the state described above isirradiated with electron beams, the unreacted portions thereof arecross-linked, and as a result, the bones as the silica can beprogressively strengthened. In addition, at the same time, micellestructures formed by the surfactant are destroyed. That is, since themicelle structures are destroyed, and the crosslinking reactionprogresses, a higher dense structure can be formed.

Next, heating (baking) is performed for the film of the dielectric rawmaterial A at 100° C. in the air (S14). This step is a step offacilitating a crosslinking reaction of the parts which are notirradiated with electron beams and is performed, for example, forapproximately 1 to 5 minutes.

Next, by using supercritical CO₂ (one example of the supercriticalfluid) at 80° C. and 15 MPa, extraction treatment is performed forhexadecyltrimethylammonium chloride which is a surfactant, so that theorganic component (surfactant) remaining in the film of the dielectricraw material is removed by supercritical extraction (S15).

In this step, for example, after the dielectric raw material is chargedinto a predetermined pressure container, followed by introduction of CO₂which is not in a supercritical state into the pressure container, thetemperature and/or the pressure is increased, so that the CO₂ is placedin a supercritical state. Alternatively, a fluid in a supercriticalstate may be charged into a pressure container in which the dielectricmaterial is placed.

Next, the dielectric raw material processed by the extraction treatmentdescribed above is heated to 200° C. in the air (S16). This heating isperformed, for example, for approximately 5 to 30 minutes. In thisembodiment, S15 and S16 are one example of the above pore forming step.

Through the steps described above, in the layer of the dielectric rawmaterial A, since parts at which the organic component was previouslypresent and was already removed are formed into pores, a layer made of aporous material is formed on the substrate (that is, one of the twoconductive plates, the conductive plate 1). In addition, compared to thepart irradiated with electron beams (that is, the part corresponding tothe dielectric strip 40), the other parts (that is, the partscorresponding to the dielectric medium layers 30) have a high porosity.When the relative dielectric constants of the layers of the porousmaterials formed by the steps described above were measured, therelative dielectric constant of the part irradiated with electron beams(that is, the part corresponding to the dielectric strip 40) was 2.0,and the relative dielectric constant of the other parts (that is, theparts corresponding to the dielectric medium layers 30) was 1.5. Asdescribed above, the dielectric strip 40 and the dielectric mediumlayers 30 are formed so as to have well-balanced dielectric constants,that is what required as the dielectric line. The dielectric strip 40and the dielectric medium layers 30 formed in this embodiment areaerogel materials (dry aerogel materials) having different porosities.

Onto the dielectric strip 40 and the dielectric medium layers 30 thusformed, the other conductive plate 2 is adhered (S17), and hence thedielectric line X can be formed.

According to the production method described above, unlike theconventional production method in which constituent elements areseparately formed, followed by assembly thereof, production can beperformed by patterning, and hence the method described above can besuitably used for mass production.

In addition, in Step 13, instead of the irradiation of electron beamsdescribed above, when irradiation of X-rays (for example, having anelectron energy of 1 GeV) or irradiation of ion beams (such as Be²⁺irradiation at an energy of 200 keV and at an ion dose of 1e¹³ to1e¹⁴/cm²) is performed, a similar result can also be obtained.

As the supercritical fluid used for the extraction treatment in S15, amixture containing two or more materials may be used, in which at leastone of the above two or more materials may be selected from the groupconsisting of carbon dioxide, ethanol, methanol, water, ammonia, and afluorinated carbon material.

Besides the materials mentioned above, a solvent may also be added inorder to improve the performance of the extraction treatment. As thesolvent to be used in this case, in view of compatibility with CO₂, anorganic solvent is preferably used. As usable organic solvents, forexample, alcohol-based solvents, ketone-based solvents, and amide-basedsolvents may be mentioned.

As particular alcohol-based solvents, for example, methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, t-butanol,n-pentanol, isopentanol, 2-methylbutanol, sec-pentanol, t-pentanol,3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, and2-ethylbutanol may be mentioned.

As particular ketone-based solvents, for example, acetone, methyl ethylketone, methyl n-propyl ketone, methyl n-butyl ketone, diethyl ketone,methyl i-butyl ketone, methyl n-pentyl ketone, ethyl n-butyl ketone,methyl n-hexyl ketone, and di-n-butyl ketone may be mentioned.

As amide-based solvents, for example, formamide, N-methylformamide,N,N′-dimethylformamide, N-ethylformamide, N,N′-diethylformamide,acetoamide, N-methylacetoamide, N,N′-dimethylacetoamide,N-ethylacetoamide, N,N′-diethylacetoamide, N-methylpropionamide, andN-methyl pyrrolidone may be mentioned.

As the surfactants mentioned above, generally known materials such asnonionic surfactants and cationic surfactants may be used. As thenonionic surfactants, for example, ethylene oxide derivatives andpropylene oxide derivatives may be used.

As the cationic surfactants, for example, quaternary ammonium salts ofan alkyl group having 8 to 24 carbon atoms, such asC_(n)H_(2n+1)(CH₃)₃N+X—, C_(n)H_(2n+1)(C₂H₅)₃N+X— (X indicates anelement to be turned into a negative ion), C_(n)H_(2n+1)NH₂, andH₂N(CH₂)_(n)NH₂ may be mentioned.

In addition, besides the materials mentioned above, there may bementioned so-called gemini surfactants which have a plurality ofhydrophilic groups and a plurality of hydrophobic groups in onemolecular, such as C_(n)H_(2n+1)X₂N+M—(CH₃)₅N+M—X₂C_(m)H_(2m+1) (n, m=5to 20). In the structure described above, X indicates an anion (inparticular, Cl⁻, Br⁻, or the like), and M indicates a hydrogen atom or alower alkyl group (in particular, CH₃, C₂H₅, or the like).

The surfactants mentioned above may be used alone or in combination.

As the dielectric raw material, an inorganic material is superior interms of heat stability, processability, and mechanical strength. Forexample, oxides of titanium, silicon, aluminum, boron, germanium,lanthanum, magnesium, niobium, phosphorous, tantalum, tin, vanadium, andzirconium may be mentioned. Among those, when metal alkoxides of theabove metals are used as the raw materials, in the film forming step,the mixing with the surfactants can be preferably performed. Asparticular metal alkoxides, for example, there may be mentionedtetraethoxytitanium, tetraisopropoxytitanium, tetramethoxytitanium,tetra-n-butoxytitanium, tetraethoxysilane, tetraisopropoxysilane,tetramethoxysilane, tetra-n-butoxysilane, triethoxyfluorosilane,triethoxysilane, triisopropoxyfluorosilane, trimethoxyfluorosilane,tirmethoxysilane, tri-n-butoxyfluorosilane, tri-n-propoxyfluorosilane,trimethylmethoxysilane, trimethylethoxysilane, trimethychlorosilane,phenyltriethoxysilane, phenyldiethoxychlorosilane,methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane,dimethyldimethoxysilane, dimethyldiethoxysilane,trismethoxyethoxyvinylsilane, triethoxyaluminum, triisobutoxyaluminum,triisopropoxyaluminum, trimethoxyaluminum, tri-n-butoxyaluminum,tri-n-propoxyaluminum, tri-sec-butoxyaluminum, tri-tert-butoxyaluminum,triethoxyboron, triisobutoxyboron, triisopropoxyboron, trimethoxyboron,tri-n-butoxyboron, tri-sec-butoxyboron, tetraethoxygermanium,tetraisopropoxylgermanium, tetramethoxygermanium,tetra-n-butoxygermanium, trismethoxyethoxylanthanum,bismethoxyethoxymagnesium, pentaethoxyniobium, pentaisopropoxyniobium,pentamethoxyniobium, penta-n-butoxyniobium, penta-n-propoxyniobium,triethylphosphate, triethylphosphite, triisopropoxyphosphate,triisopropoxyphosphite, trimethylphosphate, trimethylphosphite,tri-n-butylphosphate, tri-n-butylphosphite, tri-n-propylphosphate,tri-n-propylphosphite, pentaethoxytantalum, pentaisopropoxytantalum,pentamethoxytantalum, tetra-tert-butoxytin, tin acetate,triisopropoxy-n-butyltin, triethoxyvanadyl, tri-n-propoxyoxyvanadyl,trisacetylacetonatovanadium, tetraisopropoxyzirconium,tetra-n-butoxyzirconium, and tetra-tert-butoxyzirconium. Among thosementioned above, tetraisopropoxytitanium, tetra-n-butoxytitanium,tetraethoxysilane, tetraisopropoxysilane, tetramethoxysilane,tetra-n-butoxysilane, triisobutoxyaluminum, and trisisopropoxyaluminummay be mentioned as preferable materials by way of example. Those metalalkoxides may be used alone or in combination. As the inorganicmaterials, a material primarily composed of silica is preferably usedsince a layer having a low dielectric constant can be obtained.

Hereinafter, with reference to particular examples, superior effects ofthe present invention will be described.

EXAMPLE 1

Next, referring to the flowchart shown in FIG. 4, a first example of amethod for producing the dielectric line X shown in FIG. 1 will bedescribed.

First, a dielectric raw material B, which was a predetermined dielectricraw material, was applied to a substrate which was the conductive plate1, one of the two conductive plates described above, so as to have apredetermined thickness (S21).

The dielectric raw material B was prepared by the following procedure.After 2 g of tetramethoxysilane (metal alkoxide) Si(CH₃O)₄, which wasone example of an organic metal material, 10 g of ethanol, 2 g ofbutanol, 1 g of methyl 3-methoxypropionate, and 1.2 g of water at a pHof 3 were mixed and stirred, the mixture thus prepared was held at 60°C. for approximately 6 hours for facilitating reaction thereof to form asolution, a transparent solution was then prepared by mixing the abovesolution with IBCF (manufactured by Sanwa Chemical Co., Ltd.), which wasa photo-acid generator, at a ratio of 0.05% (percent by weight), andsubsequently, 0.2 g of hexadecyltrimethylammonium chloride (one exampleof a surfactant) was mixed whit 10 cc of the above transparent solution,followed by stirring. Next, the solution thus prepared was processed byheating (baking) at 200° C., thereby forming the dielectric raw materialB.

Next, a part coated with the dielectric raw material B described abovewas dried by heating (baking) at 80° C. in the air, so that the film ofthe dielectric raw material B was formed (S22). This heating wasperformed for a sufficient period of time (such as approximately 1 to 5minutes) to stabilize the film on the substrate by increasing theviscosity of the film. In this example, S21 and S22 are one example ofthe film forming step.

Subsequently, only a part of the film of the above dielectric rawmaterial B, which had a shape corresponding to the dielectric strip 40,was irradiated with ultraviolet rays (that is, the part having a shapecorresponding to the dielectric strip 40 was exposed to ultravioletrays) (S23).

Accordingly, Si—O bonds were formed by a crosslinking reaction.

Next, heating (baking) was performed for the film of the dielectric rawmaterial B at 100° C. in the air (S24). This step was a step of alsofacilitating a crosslinking reaction of parts which were not irradiatedwith ultraviolet rays and was performed, for example, for approximately1 to 5 minutes.

Next, by using supercritical CO₂ (one example of the supercriticalfluid) at 80° C. and 15 MPa, extraction treatment was performed forhexadecyltrimethylammonium chloride which was a surfactant, so that theorganic component remaining in the film of the dielectric raw materialwas removed (S25, one example of the pore forming step).

Onto the dielectric strip 40 and the dielectric medium years 30 thusformed, the other conductive plate 2 was adhered (S26), so that thedielectric line X could be formed.

Through the steps described above, compared to the part irradiated withultraviolet rays (that is, the part corresponding to the dielectricstrip 40), the other parts (that is, the parts corresponding to thedielectric medium layers 30) had a high porosity. When the relativedielectric constants of the layers of the porous materials formed by thesteps described above were measured, the relative dielectric constant ofthe part corresponding to the dielectric strip 40 was 2.0, and therelative dielectric constant of the other parts (that is, the partscorresponding to the dielectric medium layers 30) was 1.5.

EXAMPLE 2

Next, referring to the flowchart shown in FIG. 5, a second example of amethod for producing the dielectric line X shown in FIG. 1 will bedescribed.

First, a dielectric raw material C, which was a predetermined dielectricraw material, was applied to a substrate which was one of the twoconductor plates described above, the conductive plate 1, so as to havea predetermined thickness (S31).

The dielectric raw material C was a solution prepared by the followingprocedure. After 2 g of tetramethoxysilane (metal alkoxide) Si(CH₃O)₄,which was one example of an organic metal material, 10 g of ethanol, 2 gof butanol, 1 g of methyl 3-methoxypropionate, and 1.2 g of water at apH of 3 were mixed and stirred, the mixture thus prepared was held at60° C. for approximately 6 hours for facilitating reaction thereof so asto prepare a transparent solution, and 10 cc of this solution was mixedwith 0.2 g of hexadecyltrimethylammonium chloride (one example of asurfactant), followed by stirring.

Next, a part coated with the dielectric raw material C described abovewas dried by heating (baking) at 80° C. in the air, so that the film ofthe dielectric raw material C was formed (S32). This heating wasperformed for a sufficient period of time (such as approximately 1 to 5minutes) to stabilize the film on the substrate by increasing theviscosity of the film. In this example, S31 and S32 are one example ofthe film forming step.

Subsequently, only a part of the film of the above dielectric rawmaterial C, which had a shape corresponding to the dielectric strip 40,was exposed to vapor (S33). In this step, for example, the partdescribed above was exposed to vapor through a mask provided with awindow (opening) having a shape corresponding to the dielectric strip40, so that the other part other than the part having a shapecorresponding to the dielectric strip 40 was not exposed to vapor.

Accordingly, Si—O bonds were formed by a crosslinking reaction.

Next, after the mask was removed, by using supercritical CO₂ (oneexample of the supercritical fluid) at 80° C. and 15 MPa, extractiontreatment was performed for hexadecyltrimethylammonium chloride whichwas a surfactant, so that the organic component remaining in the film ofthe dielectric raw material was removed (S34), and heating was furtherperformed at 200° C. in the air (S35). This heating was performed, forexample, for approximately 5 to 30 minutes. In this example, Steps 34and 35 are one example of the pore forming step.

Onto the dielectric strip 40 and the dielectric medium layers 30 thusformed, the other conductive plate 2 was adhered (S36), so that thedielectric line X could be formed.

Through the steps described above, compared to the part exposed to vapor(that is, the part corresponding to the dielectric strip 40), the otherparts (that is, the parts corresponding to the dielectric medium layers30) had a high porosity. When the relative dielectric constants of thelayers of the porous materials formed by the steps described above weremeasured, the relative dielectric constant of the part corresponding tothe dielectric strip 40 was 2.0, and the relative dielectric constant ofthe other parts (that is, the parts corresponding to the dielectricmedium layers 30) was 1.5.

In addition, in Step 33, instead of the exposure to vapor oftetraethoxysilane, for example, by exposure to vapor of silicon alkoxidesuch as tetramethoxysilane, exposure to moisture vapor (such as moisturevapor at 100° C. and 1 atmospheric pressure), exposure to vapor ofanother acidic material (such as vapor of a saturated aqueoushydrochloric acid solution at 23° C. and 1 atmospheric pressure),exposure to vapor of a basic material (such as vapor of a saturatedaqueous ammonium solution at 23° C. and 1 atmospheric pressure), aresult similar to that described above can be obtained.

EXAMPLE 3

Next, referring to the flowchart shown in FIG. 6, a third example of amethod for producing the dielectric line X shown in FIG. 1 will bedescribed.

First, a dielectric raw material E, which was a predetermined dielectricraw material, was applied to a substrate which was one of the twoconductive plates, the conductor plate 1, so as to have a predeterminedthickness (S41).

The dielectric raw material E was a solution prepared by the followingprocedure. After 2 g of tetramethoxysilane (metal alkoxide) Si(CH₃O)₄,which was one example of an organic metal material, 10 g of ethanol, 2 gof butanol, 1 g of methyl 3-methoxypropionate, and 1.2 g of water at apH of 3 were mixed and stirred, the mixture thus prepared was held at60° C. for approximately 6 hours for facilitating reaction thereof toform a solution, a transparent solution D was then prepared by mixingthe above solution with IBCF (manufactured by Sanwa Chemical Co., Ltd.),which was a photo-acid generator, at a ratio of 0.05% (percent byweight), and subsequently, 0.2 g of alkyltrimethylammonium chlorideCH₃(CH₂)_(n)N(CH₃)₃Cl (in which n=12 was satisfied) (one example of asurfactant) was mixed with 10 cc of the above transparent solution D,followed by stirring.

Next, a part coated with the dielectric raw material E described abovewas dried by heating (baking) at 80° C. in the air, so that the film ofthe dielectric raw material E was formed (S42). This heating wasperformed for a sufficient period of time (such as approximately 1 to 5minutes) to stabilize the film on the substrate by increasing theviscosity of the film. In this example, S41 and S42 are one example ofthe first film forming step.

Subsequently, only a part of the film of the above dielectric rawmaterial E, which had a shape corresponding to the dielectric strip 40,was irradiated with electron beams (that is, the part having a shapecorresponding to the dielectric strip 40 was exposed to electron beams)(S43) as described in the embodiment. The amount of irradiation ofelectron beams was 10 μC/cm².

Accordingly, Si—O bonds were formed by a crosslinking reaction.

Next, for the film of the dielectric raw material E, developmenttreatment using a solvent such as an organic solvent or an alkalinesolution (such as an aqueous solution of tetramethylammonium hydroxide)was performed (one example of the film removing step). By thistreatment, in the film of the dielectric raw material E, non-irradiatedparts in which chemical bonds were not formed (that is, the parts otherthan the part having a shape corresponding to the dielectric strip) wereselectively removed.

Subsequently, a dielectric raw material F, which was a predetermineddielectric raw material, was applied onto the parts of the substrate soas to have a predetermined thickness (S45), the parts being areas atwhich the film on the substrate was removed.

The dielectric raw material F was a solution prepared by mixing andstirring 10 cc of the solution D and 0.2 g of alkyltrimethylammoniumchloride CH₃ (CH₂)_(n)N(CH₃)₃Cl (in which n=16 was satisfied) (oneexample of a surfactant).

Next, heating (baking) was performed for the film of the dielectric rawmaterial F at 100° C. in the air (S46). This step was a step offacilitating a crosslinking reaction of the dielectric raw material Fand was performed, for example, for approximately 1 to 5 minutes.

Next, by using supercritical CO₂ (one example of the supercriticalfluid) at 80° C. and 15 MPa, extraction treatment was performed foralkyltrimethylammonium chloride which was a surfactant, so that theorganic components remaining in the films (the entire films) of thedielectric raw materials E and F were removed (S47). After thisextraction treatment, heating was further performed at 200° C. in theair (S48). This heating was performed, for example, for approximately 5to 30 minutes. In this example, S47 and S48 are one example of the poreforming step.

Onto the dielectric strip 40 and the dielectric medium layers 30 thusformed, the other conductive plate 2 was adhered (S49), so that thedielectric line X could be formed.

Through the steps described above, compared to a film portion (that is,the part corresponding to the dielectric strip 40) of the dielectricmaterial E, film portions (that is, the parts corresponding to thedielectric medium layers 30) of the dielectric raw material F also had ahigh porosity. When the relative dielectric constants of the layers ofthe porous materials formed by the steps described above were measured,the relative dielectric constant of the part corresponding to thedielectric strip 40 was 2.0, and the relative dielectric constant of theother parts (that is, the parts corresponding to the dielectric mediumlayers 30) was 1.5.

In addition, except that the amount of irradiation of electron beams wasset to 5 μC/cm², a dielectric line was formed by the same method andconditions as described above. In the case described above, the partscorresponding to the dielectric medium layers 30 had a relative)dielectric constant of 1.8. As described above, by changing the amountof irradiation of electron beams, the relative dielectric constant ofthe parts corresponding to the dielectric medium layers 30 can beadjusted to an optional value.

In addition, by using a surfactant (alkyltrimethylammonium chloride) inwhich n=14 was satisfied, a dielectric line was formed by the samemethod and conditions as described above. In the case described above,the parts corresponding to the dielectric medium layers 30 had arelative dielectric constant of 1.8. As described above, the dielectricconstant of the parts corresponding to the dielectric medium layers 30can be changed.

INDUSTRIAL APPLICABILITY

As has thus been described, according to the present invention, sincethe space between the two conductive plates is filled with thedielectric strip and the dielectric medium layers, compare to theconventional dielectric line in which parts other than the dielectricstrip are composed of voids (air), the dielectric strip is not likely tobe displaced, and the strength is significantly improved to form astable structure.

In addition, since the porous materials are used for the dielectricstrip and the dielectric medium layers, by increasing the porositythereof, the dielectric constant and the dielectric loss can besignificantly decreased. As a result, high frequency signals can betransmitted with very high transmission efficiency (low loss).

In addition, according to the present invention, since being formed ofthe substantially identical porous material by adjusting the porositythereof, the dielectric strip and the dielectric medium layers can beformed from one type of material, and hence the production can be easilyperformed (reduction in production cost). In addition, since theproduction can be performed using a patterning process, compared to theconventional case in which a three-dimensional structure is produced bymachining, the mass production can be suitably performed, andcomplicated shapes can also be easily produced. Furthermore, a pluralityof dielectric strips having optional dielectric constants can be formedon one substrate (conductive plate), and hence an NRD guide capable ofresponding transmission signals having different frequencies can beformed on one substrate. As a result, the degree of freedom of designingan NRD guide is significantly increased.

1. A method for producing a dielectric line having a dielectric stripprovided between two conductive plates approximately parallel to eachother and having a width smaller than that of the conductive plates, anddielectric medium layers filled between the conductive plates other thanthe dielectric strip and composed of a porous material having adielectric constant smaller than that of the dielectric strip, themethod comprising: a film forming step of forming a film on one of theconductive plates using a dielectric raw material; a strip exposure stepof exposing a part of the film of the dielectric raw material topredetermined light, beams, or vapor, the part having a shapecorresponding to the dielectric strip; and then a pore forming step ofmaking the entire film of the dielectric raw material porous, whereinporosity of the exposed part of the film is greater than porosity of anunexposed part of the film.
 2. The method for producing a dielectricline, according to claim 1, wherein the strip exposure step is a step ofexposing the part having a shape corresponding to the dielectric stripto ultraviolet rays, electron beams, X-rays, or ion beams, and thedielectric raw material comprises a photosensitive material.
 3. Themethod for producing a dielectric line, according to claim 2, whereinthe photosensitive material comprises a photo-acid generator.
 4. Themethod for producing a dielectric line, according to claim 1, whereinthe dielectric raw material comprises an organic metal material.
 5. Themethod for producing a dielectric line, according to claim 4, whereinthe organic metal material comprises a metal alkoxide.
 6. The method forproducing a dielectric line, according to claim 1, wherein thedielectric raw material comprises a surfactant.
 7. A method forproducing a dielectric line having a dielectric strip provided betweentwo conductive plates approximately parallel to each other and having awidth smaller than that of the conductive plates, and dielectric mediumlayers filled between the conductive plates other than the dielectricstrip and composed of a porous material having a dielectric constantsmaller than that of the dielectric strip, the method comprising: afirst film forming step of forming a first film using a first dielectricraw material on one of the conductive plates; a film removing step ofremoving a part of the first film, a remaining part of the first filmhaving a shape corresponding to the dielectric strip; a second filmforming step of forming a second film using a second dielectric rawmaterial in a space from which the part of the first film was removed;and then a pore forming step of making porous the entire films of thefirst dielectric raw material and the second dielectric raw material,wherein porosity of the first film is greater than porosity of thesecond film.
 8. The method for producing a dielectric line, according toclaim 7, wherein the film removing step comprises exposing the part ofthe first film of the first dielectric raw material to predeterminedlight or beams, the part having a shape corresponding to the dielectricstrip, and then performing development treatment to remove the firstfilm other than the part having a shape corresponding to the dielectricstrip.
 9. The method for producing a dielectric line, according to claim7, wherein the first dielectric raw material comprises a photosensitivematerial.
 10. The method for producing a dielectric line, according toclaim 9, wherein the photosensitive material comprises a photo-acidgenerator.
 11. The method for producing a dielectric line, according toclaim 7, wherein the dielectric raw material comprises an organic metalmaterial.
 12. The method for producing a dielectric line, according toclaim 11, wherein the organic metal material comprises a metal alkoxide.13. The method for producing a dielectric line, according to claim 7,wherein the dielectric raw material comprises a surfactant.